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Finding the Fourth Proportional to 81, 111.69 and 78.21

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Solution

The fourth proportional to 81, 111.69 and 78.21 is: 107.84

Step by Step Solution

  1. Step 1: Write the proportion equation
    81 : 111.69 = 78.21 : x
  2. Step 2: Convert to fraction form
    81/111.69 = 78.21/x
  3. Step 3: Cross multiply
    81x = 111.69 × 78.21
  4. Step 4: Simplify right side
    81x = 8,735.27
  5. Step 5: Solve for x
    x = 8,735.27/81
  6. Step 6: Final answer
    x = 107.84

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Why These Related Problems?

These problems maintain the same ratio (1.38) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.